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Acrosome

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Jurrien Dean – One of the best experts on this subject based on the ideXlab platform.

  • Sperm binding to the zona pellucida is not sufficient to induce Acrosome exocytosis.
    Development, 2007
    Co-Authors: Boris Baibakov, Lyn Gauthier, Prue Talbot, Tracy Rankin, Jurrien Dean
    Abstract:

    At fertilization, spermatozoa bind to the zona pellucida (ZP1, ZP2, ZP3) surrounding ovulated mouse eggs, undergo Acrosome exocytosis and penetrate the zona matrix before gamete fusion. Following fertilization, ZP2 is proteolytically cleaved and sperm no longer bind to embryos. We assessed Acr3 -EGFP sperm binding to wild-type and hu ZP2 rescue eggs in which human ZP2 replaces mouse ZP2 but remains uncleaved after fertilization. The observed de novo binding of Acr3 -EGFP sperm to embryos derived from hu ZP2 rescue mice supports a `zona scaffold’ model of sperm-egg recognition in which intact ZP2 dictates a three-dimensional structure supportive of sperm binding, independent of fertilization and cortical granule exocytosis. Surprisingly, the Acrosomes of the bound sperm remain intact for at least 24 hours in the presence of uncleaved human ZP2 regardless of whether sperm are added before or after fertilization. The persistence of intact Acrosomes indicates that sperm binding to the zona pellucida is not sufficient to induce Acrosome exocytosis. A filter penetration assay suggests an alternative mechanism in which penetration into the zona matrix initiates a mechanosensory signal transduction necessary to trigger the Acrosome reaction.

George L. Gerton – One of the best experts on this subject based on the ideXlab platform.

  • acrosomal exocytosis of mouse sperm progresses in a consistent direction in response to zona pellucida
    Journal of Cellular Physiology, 2009
    Co-Authors: Mariano G Buffone, Esmeralda Rodriguezmiranda, Bayard T Storey, George L. Gerton
    Abstract:

    Sperm acrosomal exocytosis is essential for successful fertilization, and the zona pellucida (ZP) has been classically considered as the primary initiator in vivo. At present, following what is referred to as primary binding of the sperm to the ZP, the Acrosome reaction paradigm posits that the outer acrosomal membrane and plasma membrane fuse at random points, releasing the contents of the Acrosome. It is then assumed that the inner acrosomal membrane mediates secondary binding of the sperm to the ZP. In the present work we used a live fluorescence imaging system and mouse sperm containing enhanced green fluorescent protein (EGFP) in their Acrosomes. We compared the processes of acrosomal exocytosis stimulated by the calcium ionophore ionomycin or by solubilized ZP. As monitored by the loss of EGFP from the sperm, acrosomal exocytosis driven by these two agents occurred differently. When ionomycin was used, exocytosis started randomly (no preference for the anterior, middle or posterior acrosomal regions). In contrast, following treatment with solubilized ZP, the loss of acrosomal components always started at the posterior zone of the Acrosome and progressed in an anterograde direction. The exocytosis was slower when stimulated with ZP and on the order of 10 sec, which is in accordance with other reports. These results demonstrate that ZP stimulates acrosomal exocytosis in an orderly manner and suggest that a receptor-mediated event controls this process of membrane fusion and release of acrosomal components. These findings are incorporated into a model. J. Cell. Physiol. 220: 611–620, 2009. © 2009 Wiley-Liss, Inc.

  • Function of the Sperm Acrosome
    Fertilization, 2002
    Co-Authors: George L. Gerton
    Abstract:

    Publisher Summary This chapter summarizes the functions of the sperm Acrosome while assessing the currently accepted model for the states of the Acrosome during fertilization. Potential functions for the Acrosome involve issues of sperm adhesion to the zona pellucida, zona pellucida penetration, and gamete fusion. The Acrosome can be considered a compartmentalized structure. In all cases, the contents of the Acrosome are enclosed by a single, continuous acrosomal membrane that can be further delineated into two sub domains. The inner acrosomal membrane is closely opposed to the nuclear membranes, whereas the outer acrosomal membrane is present just under the plasma membrane overlying the Acrosome. The function of the Acrosome is also affected by the state of capacitation of the spermatozoa. The features of Acrosomes vary from species to species, leading some to consider that the functional importance of the Acrosome may differ between species. However, there are several common morphological, structural, and compositional properties of the Acrosome worth considering for this review. Morphologically, the spermatozoa of some non-mammalian species do not have Acrosomes, but in those spermatozoa that do, the Acrosome lies on the anterior aspect of the sperm head. Acrosome size varies remarkably from one species to the next. The acrosomal exocytosis model comprises of the following hypotheses: (1) transitional states hypothesis, (2) zona pellucida binding hypothesis, (3) zona penetration hypothesis, (4) differential release hypothesis, and (5) conservation of mechanism hypothesis.

Eduardo R S Roldan – One of the best experts on this subject based on the ideXlab platform.

  • assessment of semen quality sperm cryopreservation and heterologous ivf in the critically endangered iberian lynx lynx pardinus
    Reproduction Fertility and Development, 2009
    Co-Authors: Natalia Ganan, Eduardo R S Roldan, R Gonzalez, J J Garde, Fernando J Martinez, Astrid Vargas, Montserrat Gomendio
    Abstract:

    Semen traits and factors affecting sperm cryopreservation were assessed in the Iberian lynx (Lynx pardinus), a species regarded as the most endangered felid in the world. For cryopreservation, semen was washed, resuspended in a Tes–Tris-based diluent (TEST) or a Tris-based diluent (Biladyl), both with 20% egg yolk and 4% glycerol, loaded into straws, cooled to 5°C using an automated programmable system and frozen on nitrogen vapour. Heterologous IVF of in vitro-matured domestic cat oocytes was used to test the fertilising ability of cryopreserved spermatozoa. Electroejaculates from five males were obtained. Characterisation of the electroejaculates revealed mean (± s.e.m.) values of 3.3 ± 0.6 × 106 total spermatozoa, 73.6 ± 4.6% motile spermatozoa, 23.7 ± 4.0% morphologically normal spermatozoa and 40.7 ± 2.3% spermatozoa with intact Acrosomes. After thawing a higher percentage of motile spermatozoa was seen in TEST than in Biladyl (34.0 ± 6.2% v. 7.5 ± 4.8%, respectively; P < 0.05); however, there were no differences in the percentage of intact Acrosomes between the two diluents. Iberian lynx spermatozoa fertilised domestic cat oocytes in vitro, with higher fertilisation rates observed for spermatozoa cryopreserved in TEST than in Biladyl, although the difference did not reach statistical significance (20.5 ± 4.5% v. 11.5 ± 6.8%, respectively). There were positive significant relations between the fertilisation rates and both the percentage of normal spermatozoa and the percentage of spermatozoa with an intact Acrosome before cryopreservation (P = 0.04). This first report of the collection and cryopreservation of Iberian lynx semen and analysis of fertilising ability is an important step in the development of assisted reproductive techniques for this critically endangered felid species.

S D Johnston – One of the best experts on this subject based on the ideXlab platform.

  • semen collection ejaculate characteristics and in vitro manipulation of spermatozoa from six species of captive flying fox pteropus spp
    Reproduction Fertility and Development, 2015
    Co-Authors: D Melville, E G Crichton, S D Johnston
    Abstract:

    Seminal characteristics are described in six Pteropus species including the critically endangered P. rodricensis. Spermic ejaculates (~40 μL) were collected using electro-ejaculation on 406 of 413 attempts. All flying-fox species had mean percentages of Acrosome– and plasma-membrane (PM)-intact spermatozoa of >66% and >73%, respectively; the predominant sperm abnormalities found across all species were damaged, folded or missing Acrosomes, bent midpieces and coiled tails. Seminal pH ranged from a low of 7.5 in P. giganteus to a high of 8.2 in P. alecto with the other species in between. Electro-ejaculates recovered in short succession from P. alecto revealed no differences in sperm quality, allowing spermatozoa to be utilised for multi-treatment experiments that evaluated the effects of transportation, incubation temperature and in vitro physico-chemical environments on Acrosome and PM integrity. Pteropus alecto spermatozoa were successfully held at ~27°C and 37°C for up to 6 h before a reduction in PM integrity (P = 0.003) was observed. Acrosome and PM integrity decreased (P < 0.000) when P. alecto spermatozoa were incubated at 37°C for 30 min in a Tris–citrate buffer of pH 9.0 but remained stable at pH 5.0 to 8.0. Pteropus alecto mean (± s.e.m.) seminal osmolality was 307.0 ± 2.5 mOsm kg–1; nevertheless, spermatozoa were tolerant of media ranging from 160 to 1190 mOsm kg–1 but exposure to media of ≤160 mOsm kg–1 resulted in increased Acrosome damage (P < 0.000).

  • Semen collection, ejaculate characteristics and in vitro manipulation of spermatozoa from six species of captive flying-fox (Pteropus spp.)
    Reproduction fertility and development, 2015
    Co-Authors: D Melville, E G Crichton, S D Johnston
    Abstract:

    Seminal characteristics are described in six Pteropus species including the critically endangered P. rodricensis. Spermic ejaculates (~40μL) were collected using electro-ejaculation on 406 of 413 attempts. All flying-fox species had mean percentages of Acrosome– and plasma-membrane (PM)-intact spermatozoa of >66% and >73%, respectively; the predominant sperm abnormalities found across all species were damaged, folded or missing Acrosomes, bent midpieces and coiled tails. Seminal pH ranged from a low of 7.5 in P. giganteus to a high of 8.2 in P. alecto with the other species in between. Electro-ejaculates recovered in short succession from P. alecto revealed no differences in sperm quality, allowing spermatozoa to be utilised for multi-treatment experiments that evaluated the effects of transportation, incubation temperature and in vitro physico-chemical environments on Acrosome and PM integrity. Pteropus alecto spermatozoa were successfully held at ~27°C and 37°C for up to 6h before a reduction in PM integrity (P=0.003) was observed. Acrosome and PM integrity decreased (P

Boris Baibakov – One of the best experts on this subject based on the ideXlab platform.

  • Sperm binding to the zona pellucida is not sufficient to induce Acrosome exocytosis.
    Development, 2007
    Co-Authors: Boris Baibakov, Lyn Gauthier, Prue Talbot, Tracy Rankin, Jurrien Dean
    Abstract:

    At fertilization, spermatozoa bind to the zona pellucida (ZP1, ZP2, ZP3) surrounding ovulated mouse eggs, undergo Acrosome exocytosis and penetrate the zona matrix before gamete fusion. Following fertilization, ZP2 is proteolytically cleaved and sperm no longer bind to embryos. We assessed Acr3 -EGFP sperm binding to wild-type and hu ZP2 rescue eggs in which human ZP2 replaces mouse ZP2 but remains uncleaved after fertilization. The observed de novo binding of Acr3 -EGFP sperm to embryos derived from hu ZP2 rescue mice supports a `zona scaffold’ model of sperm-egg recognition in which intact ZP2 dictates a three-dimensional structure supportive of sperm binding, independent of fertilization and cortical granule exocytosis. Surprisingly, the Acrosomes of the bound sperm remain intact for at least 24 hours in the presence of uncleaved human ZP2 regardless of whether sperm are added before or after fertilization. The persistence of intact Acrosomes indicates that sperm binding to the zona pellucida is not sufficient to induce Acrosome exocytosis. A filter penetration assay suggests an alternative mechanism in which penetration into the zona matrix initiates a mechanosensory signal transduction necessary to trigger the Acrosome reaction.